- Voltage: potential difference between 2 points in a circuit - Current: flow of charge, $1A=1C/s$ - $i=\frac{dQ}{dt},Q=\int i~ d{t}$ - Power: circuit energy, 1W = 1J/s - $P=\frac{E}{t}=VI$ - Resistance: constricts current flow, used to dissipate energy, given by $\Omega$ - In this class, a wire conducts current, has 0 voltage & 0 resistance (~negligible) - Bottom wire is always gnd (0V) # Energy sources - Independent energy source: does not depend on any other circuit parameter - Dependent source: does depend on another circuit parameter - Passive sign convention: current flows out of positive(+) terminal of voltage source - Current flows $+\to-$ through an element (resistor, capacitor, inductor,..) - Flipping direction of current negates its value - Flipping polarity of source changes negates the value ## Power absorbed/delivered - For a voltage source, delivers power if current leaves positive terminal - depends on direction of current flow relative to voltage polarity - In general always draw current coming out of positive terminal - Absorbs power if current enters element through positive terminal - Power absorbed: $P>0$ & vice versa # Open v. Short circuit - Open circuit: no current flow w/ only potential difference ($\therefore$ voltage), caused by an opening in circuit - $i=0,R=\infty$ - Short circuit: wire, no resistance w/ current flow and no voltage - closed flow - Current prefers the path of least resistance - Element $\parallel$ wire cancels out -> current prefers path of least resistance # Parallel v. Series Circuits - Series: elements connected end-to-end (1 common node) - Same current for all elements - Different voltage for all elements - Parallel: elements connected at 2 common nodes - Same voltage for all elements - Different current for all elements # Resistance & Ohm's Law - $V=IR$ - Resistance: describes how much an element opposes current flow - Resistor power: $P=I^2R=\frac{V^2}{R}\text{ (W)}$ - Conductance: $G=\frac{1}{R}\text{ (Siemens)}$